1. Field of the Invention
This invention relates to the field of heart surgery. More specifically, this invention relates to a cavo-atrial cannula, used to remove blood from the body while performing surgery on the heart, and the method of using such a device. This invention is a single cannula, introduced into the right atrium via the superior vena cava or inferior vena cava, thereby avoiding an incision in the right atrium.
2. Description of the Related Art
During cardiopulmonary bypass for heart surgery a mechanical device, a pump oxygenator, drains the patient's blood, oxygenates it, and returns it to the patient through tubing connected to cannulae placed in the patient's heart and aorta. Typically, drainage is accomplished by a single venous cannula, possessing two sets of openings, placed through an incision in the right atrium and secured in place by a pursestring-suture tourniquet applied along the edges of the atrial incision such that the cannula tip lies in the inferior vena cava. The set of openings at the cannula's terminus drain blood from the inferior vena cava, and the openings proximal to it drain the blood which has arrived from the superior vena cava and other lesser sources into the right atrium. An alternative method uses two venous cannulae, one directed into the superior vena cava and the other into the inferior vena cava. One or both of these cannulae are introduced through incision(s) in the right atrium.
The currently used venous cannulae and the methods by which they are placed in the heart present certain problems. The right atrium suffers significant damage not only from of the incisions made to introduce the cannula(e) but also because of the right atrium's relative inaccessibility to the protective measures used to preserve heart tissue functional integrity during surgery. These protective measures consist primarily of drugs, such as cardioplegic solutions, infused into the blood supply of the heart tissue to arrest beating, as well as the constant topical application of ice-cold saline on the surface of the arrested heart. The method by which the cannulae are currently placed in the right atrium prevents the protective drugs from reaching the atrial tissue constrained in the tourniquet. Furthermore, the atrial tissue at the entry site of the cannula escapes the cold saline bath inasmuch as the atrial tissue is suspended upward out of the chest by the outward course of the cannulae toward the pump oxygenator. The functional consequences of direct injury to the atrial tissue as well as the sub-optimal access to the protection afforded to the rest of the heart include decreased strength of contraction and, perhaps more importantly, disordered atrial rhythm, e.g., atrial fibrillation, which can cause poor cardiac function, blood clots, and dangerously high heart rates. The drugs used to treat atrial fibrillation also have an array of potentially dangerous side-effects. The economic costs of atrial dysfunction reflect the price of the drugs used to treat it, longer hospital stays, and the additional hospital admissions for related complications.
Currently available cannulae can not be inserted into the vena cava for drainage of blood from the vena cava and right atrium for three reasons. First, most currently available cannulae have too narrow a diameter for adequate venous drainage and to maintain adequate flow of blood from the patient. Second, even if the diameter of the currently available cannulae were enlarged enough to maintain adequate flow of blood from the patient, the placement of such enlarged diameter cannulae in the superior vena cava would cause significant obstruction to blood flow from the head and upper body which normally courses through the superior vena cava into the right atrium. Similarly, enlarged diameter cannulae can not be inserted into the inferior vena cava because the placement of such cannulae in the inferior vena cava would cause significant obstruction to blood flow from the lower body which normally courses through the inferior vena cava into the right atrium. Third, currently available cannulae contain circumferential openings. If a circumferential opening lies just within the vena cava, then it would increase the risk of entraining air into the pump circuit, causing an "air lock" and obstruction to flow.
The placement of the openings in the currently available cannulae are not appropriate for effective drainage of the blood flowing down the superior vena cava when the cannulae are inserted through the superior vena cava nor for effective drainage of the blood flowing up the inferior vena cava when the cannulae are inserted through the inferior vena cava. Usage of currently available cannulae for drainage of blood through the superior vena cava would cause obstruction of the blood flow and could cause swelling of the brain, neurological dysfunction, and stroke. Obstruction of inferior vena cava blood flow could cause congestion and dysfunction of the abdominal organs.